Alloy steel



Patented May 14, 1940 STATES ALLUY STEEL Edgar F. Blessing, Short Hills,N. 56., assignor to Chas. W. Guttzeit, New York, N. Y.

No Drawing.

l4 Glaims.

Another object is to provide a steel of this type 15 having a lowhardening temperature.

Another object is to provide a high quality steel having eflective redhardness at unusually high temperatures.

It has been discovered in accordance with the 20' invention thatifmolybdenum and chromium are combined in the steel in relatively highproportions and in proportions such that the proportion of chromiumandthat of molybdenum are not too widely different then a desiredtoughness and hardness, together with the property of hardening at arelatively low hardening temperature is given to the steel. 'Ithas alsobeen discovered that in such steels the'tendency to decarburize and/ordemolybdenize at high temperatures is 30 substantially eliminated orvery much reduced. The chromium appears to serve as a carrier for themolybdenum and possibly causes a thin film of chromium or mixed oxide onthe surface which inhibits decarburization and demolybdenization. For adie steel the proportion of chromium should preferably be substantiallyequal to or greater than but not more than about 25% or perhaps 50%greater than the proportion of molybdenum and for a tool steel theproportion of molybdenum should preferably be substantially equal to theproportion of chromium or between the proportion 3:2 and 2:3 andprobably between the proportions :4 and 4:5.

Molybdenum and tungsten have been used I 45 heretofore in steels asalloying ingredients and have even been combined with chromium withvarying success. However, the steels produced have been of other typesthan that of the present invention or'the proportions and quantities ofmolybdenum and chromium necessary to obtain the results of the presentinvention have not been maintained. Inv fact, experiments heretoforemade have indicated that a steel of the type produced by the presentinvention must not contain so large a proportion of chromium and ofmolybdenum as has now been found highly effective. High tungsten steelsare rendered brittle by high percentages of chromium and metallurgistshave heretofore believed that in high speed steels generally it wasnecessary to avoid Application November 11, 1937, Serial No. 174,009

the presence of more than about 5% of chromium when good forgeabilitywas required. It is an important discovery of the present invention thatwith the higher percentages of molybdenum and low percentages oftungsten, high percentages of 5 chromium do not render the steelbrittle, but on the other hand give a surprisingly better forgeablesteel having the remarkable quality of resisting decarburizationanddemolybdenization. Applicants experiments indicate that chromiuminproper percentages has a pronounced effect in bringing out the.hardening and heat resisting properties induced by molybdenum andtungsten in these alloys, and that when large percentages of chromium,as 8, or better 9, to 17% are combined with large percentages ofmolybdenum, as 8, or better 9, to about 15% and small percentages oftungsten as up to 2 or 5%, the full effect of these elements andparticularly of the molybdenum is brought out and intensified and bettercutting and heat resisting, that is to say, scale resisting and redhardness, properties are given to the steel. It is believed that theaddition of chromium with the molybdenum and tungsten and especiallywith the addition of chromium in 2 a proportion not greatlydifierentfrom that of the molybdenum has the effect of increasing thesolubility of the molybdenum in iron and for this reason improves thequality of the alloy. The solubility of the molybdenum carbide, tungstencarbide. mixed carbides and iron carbide is believed also to be improvedand in any event it is found that the steel can be properly hardened atlower temperatures, (below 2200 F.) as for example at temperaturesbetween 1800 and 2100 F.

Cobalt when combined with large percentages of chromium and ofmolybdenum in the steel of the present invention adds toughness,increases the resistance to checking at hightemperatures and improvesthe cutting qualities.

It is one of the peculiar developments of the invention that the cobaltappears to reduce the hardening temperature or at least does notincrease it. The herein described chromium-molybdenum-tungsten steelscontaining, for example, 3 to 12% cobalt with less than 2% tungsten arefound to develop the amazing property of hardening at comparative lowtemperatures (about 1800 to 2050 F.). This is very striking whencompared to the tungsten series such as the 18-4--1 high speed steels inwhich when increasing quantities of cobalt are added we find a-tendencyfor hardening temperatures to increase. For 'example, for 18-41 steelthe recommended hardening temperature for best re-v sults is 2300 to2350 F., but when 12% cobalt is added to this steel the recommendedhardening temperature is 2400 to 2500 F. The high cobalt, molybdenum,chromium steels of this seno Per cent by weight- Molybdenum 8 15Tungsten 0 5 Chromium 8 17 Vanadium 0 5 Carbon 0.20- 1.50 Silicon 0 1.50Manganese 0 1.50 Cobalt 0 15 Iron The remainder ries with tungsten willbecome increasingly austenitic and the temperature required to producethis condition appears to be progressively lowered as the percentage ofcobalt is increased, provided the tungsten content is low, and at thesame time if a steel having initially an austenitic condition isdesired, it may be hardened at a comparatively low temperature withoutsacrificing its property of developing a secondary hardness withincreased minerological hardness at unusually high drawing temperatures.When the steels described are quenched from the higher hardeningtemperatures as about 2000 to 2100" F. austenitic structure results. Asecondary hardening or precipitation hardening of steels so ,hardened,as also steels hardened at lower temperatures, can be obtained bydrawing at temperatures of about 1000 to 1200 F. or even higher. Ahardness of about (7-60 to C- for steels herein described can beobtained if the hardening temperature is well chosen for this result.When the austenitic structure is obtained the hardness may be below C-50or even below (3-40 but a high secondary hardness, for example aboutC-55 may be obtained by re-heating to the temperatures above indicatedand especially by holding the steel at such temperatures for severalhours. A little experimenting with sample pieces of the steel enablesone to determine the optimum reheating temperatures. The steels of theinvention, especially steels having the higher percentages of cobalt,hardened and reheated as above indicated, are surprisingly durable forhot work. For certain work it is advantageous to draw hardened tools attemperatures of 1000 to 1300 or 1400 F. for 5 to 35 hours depending uponthe degree of precipitation and hardness desired.

Certain other alloying ingredients commonly used in die steels and inhigh speed steels may also be added for their usual effects withoutimpairing the effect of the molybdenum and chromium or losing theadvantages thereof. It is particularly desirable to add a smallproportion of vanadium for example 0.1 to 3% or even 5% to increase thetoughness.

The improved steel may contain, for example:

The steel of the present invention is particularly suitable for dies andfor high speed hot-hard tools. If the steel is to be used for dies acomposition such as the following may be used:

Efiective Preferred composition composition Percent Percent MolybdenumH; 8 12 11 Tungsten 0 2 0 20- 2 Chronnum r 8 15 8 l2. 50 Vanadium 0 2.50 0 50- 2 0.20- 0. 80 0 20- 0.65 0.15- 1.50 0.75- l 25 0.15- 1.50 0.30-0 75 0 15 0. 50-13 The remainder The remainder More specifically, forcertain types of dies a steel of this composition having a chromiumcontent of 8.5 to 10% with 8 to 10% molybdenum and not more than 1% oftungsten provides especially satisfactory durability. If the die is moreof the nature of a cutting tool, the carbon should be raised. Thefollowing illustrate representative stee1s Percent Percent PercentMolybdenum 8. 50-9 9. 50-11 9. 50-10. 50 Tungsten 0. 25-2 0. 25-1 0.25-1 Chromium 8 8. 50 8 8. 50 9. 50-10. 60 Vanadium. 0. 50-1 0.50-2.500.50- 2. 50 Carbon 0. 30-0. 50 0.25-0.60 0. 20- 0.70 Silicon 0. 75-1.100. 76-1. 10 0. 75- 1.10 Manganese 0. 40-0. 0.35-0.75 0. 35- 0.75 Cobalt0. 50-1 0. 50-7 11. 50-12. 50 Iron The remainder The remainder Theremainder Per- Per- Percent cent cent Molybdenum 8. 50 9.25 8.50Tungsten 1 2 0. 25 Chromium 8. 50 10 8.50 Vanadium". 1. 50 1.50 1.75Oarbon. 0.65 0.80 0.75 Silicon... 0.75 0. 0. 30 Manganese 0. 50 0. 500.30 Cobalt 4 0 3. 50 Iron The remainder Eflective composition Preferredcomposition Percent Percent 8 0 5 8 17 8 0 5 0. 0.50- 1.75 0 1.50 0Manganese 0 1. 50 0 Cobalt 0 15 Molybdenum 3 Iron The remainder Morespecifically, for metal forming tool steels of this compositioncontaining 8-10% chromium and 8.50 to 10% molybdenum are extremelyduraable. The following examples illustrate representative steels-Percent Percent Percent Molybdenum... 8. 50-9 8. 50-9 9. 50-10 0. 50-2 00. 50 0. 60- 2 8 8. 50 8. 50-9 9 -10 1. 40-1. 75 1. 25-2 1 2 0. 75 1. 250. 75-1 0. 75- 1 0 1. 10 0 1 0 l Manganese 0 1. l0 0 -1 0 1 obal 3. 50-43 -4 3 4 Iron The remainder The remainder The remainder Percent PercentPercent Percent Molybde- 8.50 11 10.50 10.50

num. Tungsten 1 0. 25 1'. 50 0. 50 Chromium 8. 50 11 11 10. 50Vanadium. 1. 50 1. 50 1. 50 2 Carbon 0. 0.95 1 1 Silicon 0. 50 0. 50 0.50 0. 50 Manganese. 0. 50 0. 50 0. 50 0. 50 Co a t 3. 50 4 5 13 Iron TheThe The The remainder remainder remainder remainder In these steels thevanadium can be increased to 3 or even 5% to advantage for certaintypesof metal working tools requiring sharp and durable cutting edges. Thecobalt may also be raised as to 7 or 12% to provide greater toughnessand improved cutting qualities as in other similar steels. The steel ofthe last example above having about 10.50% molybdenum, 10.50% chromiumand 13% cobalt can be hardened by quenching from a temperature below1900 F.

The principle of increasing the chromium with high molybdenum may beeffectively applied to very high cobalt steels. Such a steel maycontain- Per cent Molybdenum 8 9 Chromium 8 9 Vanadium 1.50 Carbon 0.10-0.30 Cobalt 34 -37 Iron The remainder Where good forgeability isrequired the maximum carbon should not be used with the maximum limitsin chromium and molybdenum shown for my alloy. The maximum limits ofmolybdenum, chromium and cobalt have not been ascertained by experimentbut the experiments made indicate that up to about 13% molybdenum, about15% chromium and about 15% cobalt are permissible in forgeable steels.

Higher carbon is necessary with high molybdenum, low tungsten and highchromium for the reason that the steel is progressively softer afterheat treatment as the chromium is increased. The increase of chromiumfrom 8.50 to 10.50% will require an increase in the carbon content ofabout 0.25% to obtain the same relative hardness, for example in a steelfor cutting tools.

The cobalt toughens the steels above described. Cobalt up to about 4% ina steel containing about 8.50 chromium, about 8% molybdenum and about 1%tungsten toughens the steel to improve I its shock resistance togetherwith some improvement in the quality of its cutting edge. About '7 or7.50 to about 12% or perhaps 15% cobalt substantially improves thecutting quality and generally in proportion to the amount added.

I Because of the low hardening range (1800 to 2050 F. or in some cases2150 F.) of these steels containing 8% and more of both chromium andmolybdenum with up to 2% tungsten and 0.1 to 12% of cobalt or more it ispossible to hold and "soak these steels at or near this range oftemperatures for a long period of time to cause the solution of thecarbides without the risk of burning and severe scaling as would be thecase when long heating and soaking at temperatures of 2150 to 2500 F.are used as for other types of high speed tool and die steels.

may be added to the above described alloy without sacrificing theadvantageous features of the invention except as, in some cases, theyincrease the cost of the steel, when desired to give to the steel thequalities which these high melting metals are known to give. Vanadiumalready mentioned has the effect of raising the drawing temperature,

toughening the steel and improving its cutting qualities. Uranium up to3% has an effect substantially similar to the effect of vanadium.Tantalumup to 10% increases the initial hardness of the steel whenquenched and raises the temperingtemperature. The tantalum forms stablecarbides and therefore adds to the hardness. Such formation of carbidesmay make desirable an increase in the total carbon content. Columbium upto 10% toughens the steel. Titanium' or zirconium up to 3% increases thehardness obtained upon quenching and increases the hardening and drawingtemperatures while it also tends to make the steel brittle. Nickel up toreduces the hardening temperature and reduces the initial hardness butit does not affect the drawing temperature. It tends to make the alloytougher but increases the hot shortness. The preferred steels made toembody the principles of the invention do not contain more than about 5%of the above high melting point metals.

The steels described have the decided advantage that they can beproduced at much less cost than high tungsten steel having more or lesssimilar properties and yet when containing the preferred proportions ofthe alloying metals they are for many purposes as good as or decidedlysuperior to more expensive steels heretofore produced.

It seems from examination of tools after use that the high chromium andhigh molybdenum high speed steel herein described has a particularly lowgalling property under the chip as shown by the smooth condition of theedge of the tool after cutting. This may account in part for the greatercutting efllciency of the high chromium, high molybdenum, low tungstensteel as compared with 18+-4-1,high speed steel.

The low chromium molybdenum tungsten steels (containing 4% chromium)must be hardened or heat treated in special atmospheres furnaces toovercome the marked tendency to decarburize and demolybclenize'or theymust be protected by a coating of borax or the like with all of-th'einconvenience and expense that this involves. In marked contrast to thisthe high chromium steels of the present invention can be heated infurnaces without atmosphere control for hardening and hot working andcan be worked at high temperatures without perceptible deterioration ofsurfaces or sharp edges.

This feature of preventing decarburization and demolybdenization, isespecially valuable in greatly simplifying manufacturing processes sincethe low chromium-molybdenum steels have also a marked tendency to loseaconsiderable proportion of their carbon and molybdenum at the surfacewhen being rolled and forged. The decarburization and/ordemolybdenization frequently extends to a depth of and more, dependingon the time at heat. Chromium, when used in substantially equalproportions with molybdenum, in steels of the type under consideratlon,particularly when these two elements are in excess of 8% each, has theextremely valuable effect of inhibiting decarburization anddemolybdenization. It almost, if not quite, entirely prevents this.Naturally, the absence of decarburization and demolybdenization at thesurface of tools made from it greatly increases the surface hardness andtherefore, the effective cutting qualities of these tools as comparedwith tools of molybdenum steels containing 8.50% of molybdenum or morewith only 3-5% of chromium.

The higher chromium, 8% and over, especially in combination with themolybdenum of 8% and more, greatly increases the scale resistance ofsuch steels. This condition, unlike the case of the low chromiummolybdenum steels, permits the high chromium (8% or more) molybdenumsteels to be hardened in the ordinary standard type of heat treatingfurnace used for high tungsten high speed steels and othernon-molybdenum tool and die steels.

It should beemphasized that a valuable eflect of. the high chromium .(8%or more) and particularly 9% or more, with 8% and more of molybdenum, isfound in the lowering of the effective hardening temperature necessaryto obtain full hardness of the steel. For example, a steel containing.'79% carbon, 8.92% molybdenum, 0.35% tungsten, 0.98% vanadium and 3.31%chromium requires a temperature of 2150-2250 F. for full hardeningwhereas steels of the present invention can be fully hardened whenquenched from temperatures below 2100 F. Experiments have establishedthat many of the steels compounded in accordance with the invention and.within the range 8-11% molybdenum, 0 to 2% tungsten, 8-11% chromium,0-3% vanadium, 0-l5% cobalt, and 0.2-1.50% carbon have hardeningtemperatures between 1800 and 2000 F. For example, steels containing10.50 to 11% molybdenum, less than 1% tungsten, 10.50 to 11% chromium,up to 15% cobalt and the necessary carbon within the range of 0.75 to1.25% have a hardening temperature for full hardening at about 1800 to1900 F. This represents a considerable advantage over 2350 F. requiredfor.

full hardening of the standard 18-4-1 high speed steel, and over 2500 F.required for full hardening of the standard l8-4-1 steel with 12%cobalt. The value of this lower hardening temperature in hardeningtools, especially tools having fine edges, will prove to be very greatin the manufacture of such tools because of the elimination of thehazard of breakage and burning or wasting of the fine edges.

The expression complete hardening is used herein to define the ordinaryhardening that is satisfactory in use in dies, cutting tools and thelike and is obtained by quenching from what are commonly referred to ashardening temperatures, but the use of this language is not intended tomean that the same steel may not be hardened to a slightly greaterhardness by special heat treatment, nor that other heat treatments maynot be found which will produce a slightly greater degree of hardness.

The term tool as used in the claims is used in its broad significance toinclude dies as well as other tools.

The term hot working is used to include both rolling and forging.

The expression the remainder substantiallyall iron as used in the claimsis intended to include,

in addition to iron, minor impurities and small proportions of alloyingelements not sufficient to change the general character of the steel ordestroy the advantages of the combination of molybdenum, tungsten andchromium in the proportions defined.

It is contemplated that variations from the illustrative compositionswill be made in accordance with well understood metallurgical principleswithout departing from the spirit of the in vention or sacrificing theadvantages thereof. The proportions stated are not intended as defininglimits beyond which none of. the benefits of the invention can beobtained. The high chromium content gives high resistance to corrosionand stain. The composition is such that the steel can be effectivelynitrided to provide great surface hardness for certain uses as forexample for drawing dies. Furthermore, suitable additions of titanium,above suggested, or of aluminum may be included when the steel is to benitrided.

This application is a continuation in part of applicants co-pendingapplication Serial No. 51,224 filed November 23, 1935, now Patent No.2,099,509 granted November 16, 1937.

I claim:

1. A forgeable steel characterized by being substantially stable againstdecarburization and demolybdenization at its hot working and hardeningtemperatures comprising as its principal alloying ingredientsapproximately 8.50% molybdenum, 8.50% chromium, 1% tungsten, 4% cobalt,0.75 to 1.50% vanadium and 0.30 to 0.65% carbon, with the remaindersubstantially all iron.

2. A forgeable steel characterized by being substantially stable againstdecarburization and demolybdenization at its hot working and hardeningtemperatures and by being capable of complete hardening when quenchedfrom a hardening temperature below 2050 F., comprising as its principalalloying ingredients approximately 8 to 10% molybdenum, 8.50 to 9%chromium, an effective amount up to 2% tungsten, an effective amount upto 5% cobalt, an effective amount up to 3% vanadium and 0.20 to 1.50%carbon, with the remainder substantially all iron.

3. A'forgeable steel characterized by being substantially stable againstdecarburization and demolybdenization at its hot working and hardeningtemperatures and by being capable of complete hardening when quenchedfrom a harden-- ing temperature below 2100 F. comprising as itsprincipal alloying ingredients approximately 8 to 10% molybdenum, 8.50to 9% chromium, an efiective amount up to 2% tungsten and 0.20 to 1.50%carbon; the major portion of the remainder being iron.

4. A forgeable steel comprising as its principal alloying ingredients,approximately 8 to 10% molybdenum, chromium suflicient in amount topractically prevent decarburization and demolybdenization of the steelat its hot working and hardening temperatures, said chromium being morethan 8% and not substantially more than an effective amount up to 2%tungsten,

an effective amount up to 4% vanadium and i 0.20 to 1.50% carbon, themajor portion of the remainder being iron.

5. A forgeable steel characterized by being substantially stable againstdecarburization and demolybdenization at its hot working and hardeningtemperatures and by being capable of complete hardening when quenchedfrom a hardening temperature below 2050" F., comprising as its principalalloying ingredients approximately 8 to 10% molydenum, 8.50 to 10%chromium, an effective amount up to 1% tungsten, an effective amount upto 3% vanadium and 0.20 to 0.80% carbon, the major portion of theremainder being iron.

6. A forgeable steel characterized by being substantially stable againstdecarburization and demolybdenization at its hot working and hardeningtemperatures, comprising as its principal alloying ingredientsapproximately 8 to 13% molybdenum, 8 to 10% chromium, an efiectiveamount up to 2% tungsten, an effective amount up to 15% cobalt, aneffective amount up to 3% vanadium and 0.20 to 1.50% carbon, with theremainder substantially all iron.

7. A forgeable steel comprising as its principal alloying ingredientsapproximately 8 to 13% molybdenum, chromium suflicient in amount topractically prevent decarburization and demolybdenization of the steelat its hot working and hardening temperatures, said chromium being morethan 8% and not substantially more than 10%, an effective amount up to2% tungsten, an effective amount up to 3% vanadium and 0.20 to 1.50%carbon, the major portion of the remainder being iron.

8. A forgeable steel comprising as its principal alloying ingredientsapproximately 8 to 13% molybdenum, chromium sufficient in amount topractically prevent decarburization and demolybdenization of the steelat its hot working and hardening temperatures, said chromium being morethan 8% and not substantially more than 10%, an efiective amount up to2% tungsten and 0.20 to 1.50% carbon, the major portion of the remainderbeing iron.

9. A forgeable steel characterized by being substantially stable againstdecarburization and demolybdenization at its hot working and hardeningtemperatures and by being capable of complete hardening when quenchedfrom a hardening temperature below 2050 F. comprising as its principalalloying ingredients approximately 8 to 13% molybdenum, 9 to 12%chromium, an effective amount up to 2% tungsten, and 0.75 to 1.15%carbon, the major portion of the remainder being iron.

10. A forgeable steel characterized by being substantially stableagainst decarburization and demolybdenization at its hot workingtemperature and by being capable of complete hardening when quenchedfrom a hardening temperature below 2100 F. comprising as its principalalloying ingredients approximately 8 to 13% molybdenum, more than 8% butnot more than 15% chromium, an efiective amount up to 5% tungsten, anefiective amount up to 15% cobalt, 0.20

up to 4% vanadium and 0.20 to 1.50% carbon,

the major portion of the remainder being iron.

12. A forgeable steel characterized by being substantially stableagainst decarburization and demolybdenization at its hot working andhardening temperatures and by being capable of complete hardening whenquenched from a hardening temperature below 1900 F. comprising as itsprincipal alloying ingredients approximately 9.50 to 11% molybdenum,9.50 to 11% chromium, an effective amount up to 0.50% tungsten, 11 to15% cobalt, 1.50 to 2.50% vanadium, and 0.80 to 1.15% carbon, with theremainder substantially all iron.

13. A forgeable steel characterized by being substantially stableagainst decarburization and demolybdenization at its hot working andhardening temperatures, comprising as its principal alloying ingredientsapproximately 9 to 11% molybdenum, 9 to 11% chromium, an effectiveamount up to 0.75% tungsten, 0.50 to 2% vanadium and 0.30 to 1.15%carbon, the major portion of the remainder being iron.

14. A iorgeable steel comprising as its principal alloying ingredientsapproximately 8 to 9.25% molybdenum, chromium suflicient in amount topractically prevent decarburization and demolybdenization of the steelat its hot working and hardening temperatures, said chromium being morethan 8% and not substantially more than 10%, 2% tungsten, 0.90 to 1.50%vanadium and 0.60 to 0.90% carbon, the major portion of the remainderbeing iron.

EDGAR F. BLESSING.

